This invention relates to a compression release mechanism for internal combustion engines, and more particularly to an automatic compression release mechanism that is responsive to the temperature in the combustion chamber of the engine.
Compression release mechanisms are frequently used with small gasoline engines, such as those used on lawn mowers, to reduce the manual force required to start the engine and to eliminate the danger of physical injury from kickbacks. The primary concern of such a device is to facilitate starting of the engine without sacrificing the proper choke conditions for starting at cranking speeds and without impairing the normal power performance of the engine at running speeds.
Various arrangements for releasing compression during starting are known in the art. A common type of compression release mechanism is associated with the cam shaft and includes a centrifugal member which, during starting, will hold the exhaust valve open to release compression, and once the engine has started, centrifugal force will act upon the member to permit the valve to operate in a normal manner. Examples of such devices may be found in U.S. Pat. Nos. 3,314,408, 3,620,203, 3,901,199 and 3,981,289. These types of compression release mechanisms, however, require multiple parts that have relatively complicated shapes, or require special tooling and/or modification of the cam shaft for installation.
Another type of compression release mechanism is shown in Roorda, U.S. Pat. No. 3,335,711. The Roorda patent shows a valve that controls compression pressure through a release passage which is connected to the combustion chamber of the engine and is manually opened during cranking and is automatically closed on the first firing stroke of the engine. However, these types of valves require multiple parts, and their manual operation may be overlooked by an operator of the engine.
The prior art also teaches the use of a pair of reed valves as a compression release mechanism in Perlewitz, U.S. Pat. No. 3,417,740, and the use of a small restricted passageway in the cylinder wall which is continuously open in Grisbrook, U.S. Pat. No. 3,040,725. None of these arrangements, however, have been found to solve the problem of providing a reliable compression release mechanism having a minimum number of moving parts.